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This article will focus on a narrow aspect of the larger question of the effect of international economic integration and increased international security on the national legal order of complex states, such as the United States and Spain. At first glance, the United States and Spain have rather different systems of constitutional law concerning the relationship between the center and periphery. Nonetheless, as this article will argue, it is revealing to explore the recent responses of theories as different as U.S. federalism and Spain's system of autonomous communities to the new international environment in the crucial area of the external activities of sub-state entities. In this way, one can begin to understand the extent to which centripetal and centrifugal forces described above may influence constitutional systems generally.

This article therefore will begin with a comparison of common law and the continental system of legal science, which in each constitutional system operate as a lens through which one can study the substance of constitutional and international law (and, in the case of Spain, also supranational law). These conceptual lenses are necessary for readers or students of both systems to translate the opinions of the U.S. Supreme Court and Spain's Constitutional Tribunal into their respective legal vocabularies. Once these concepts are explicated, it will be possible to analyze the similarities and differences between federalism's organizing concept of dual sovereignty and Spanish autonomy's organizing concept, in my view, of a version of subsidiarity.

Thereafter, this article will apply these concepts to the jurisprudence of the U.S. Supreme Court and Spain's Constitutional Tribunal concerning the external activities of sub-state entities, and then it will conclude with some brief comments concerning the significance of these constitutional developments for the state of international law and the comparative study of constitutional law, in particular the relative value of constitutional law methodologies grounded in common law and civil law in responding to international system change.



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